The proposed study is based on the following observations from our previous work: (i) Certain peripheral white blood cells possess cell surface DNA (csDNA), based on the binding of a radioactive DNA probe - viz lactoferrin. (ii) When cells are stripped of their csDNA (by DNAse) they will take up exogenous DNA (3H labelled) in a saturable manner consistent with a ligand receptor relationship - for monocytes and neutrophils the Kd is about 2.5 x 10-billion M and some 1 to 2.5 x 1 million molecules of lambda phage DNA bind per cell. (iii) Using a biotin labelled DNA probe we have demonstrated a DNA binding protein in an SDS-PAGE preparation of neutrophil surface membranes; the MW of this putative DNA receptor was about 30,000. (iv) Preliminary studies of 3H DNA binding in normals and patients with connective tissue diseases indicates that some patients with systemic lupus erythematous (SLE) have an apparent DNA-receptor defect. It is intended to expand these findings as follows: (i) Establish which cell populations are capable of binding DNA; (ii) Verify that the binding is a saturable phenomenon with a Kd consistent with a ligand-receptor association; (iii) Determine whether bound DNA is internalized, and if so, if it is further degraded; (iv) Study factors influencing receptor turnover and regeneration; (v) Analyze purified membrane preparations from different cell types (using the biotin labelled DNA probe/PAGE system) for DNA binding proteins; (vi) Study the prevalence of deficient DNA binding in patients with SLE and see if this correlates with disease activity, serological markers inherited complement deficiencies or HLA typing; (vii) Look for abnormal DNA binding in other connective tissue disorders, other chronic diseases and normals; (viii) Try to determine whether deficient DNA binding is due to a receptor defect or a serum blocking factor. The definitive demonstration of a DNA receptor on certain immunocompetent cells would have important implications for molecular biology in general, and the confirmation of a receptor defect in SLE would open up a new avenue of research into the pathogenesis of this prototypical autoimmune disease.